The present invention relates generally to a UV phototherapy apparatus and method for treatment of dermatoses or skin diseases such as psoriasis, vitiligo, eczema, rosacea, alopecia, and the like, and is particularly concerned with a targeted UV phototherapy apparatus and method in which radiation is applied to successive specific areas of a lesion.
Phototherapy is the use of ultraviolet radiation to achieve therapeutic benefit to dermatoses (psoriasis, vitiligo, rosacea, alopecia, eczema). The UV spectrum is divided into UVA (320-400 nm), UVB (290-320 nm) and UVC (100-290 nm). The UVA region is considered the longwave UV spectrum responsible for tanning effects, the UVB region is considered the sunburning region (erythemal region), and UVC is considered the germicidal region. Typically, both UVA and UVB radiation has been used for treatment of dermatoses. Treatment with UVA radiation is called photochemical therapy and involves the use of a photosensitizing agent, psoralen, and the administration of UVA radiation. The basis for phototherapy is believed to be the direct interaction of light of certain frequencies with tissue to cause a change in immune response. U.S. Pat. No. 5,696,081 of Ullrich describes the immune response caused by UVA and UVB radiation.
Phototherapy has a long history of treating psoriasis dating back to 1926 when natural solartreatments such as the Goekerman regimen and Heliotherapy (sunlight rich in UVB at the Dead Sea) were practiced. Heliotherapy is still practiced today. However, these natural solartreatments have mostly given way to modern booths or chambers that provide artificial UVA and/or UVB radiation. Although the benefits of UVA and UVB are known in dermatoses treatment, the adverse affects upon healthy tissue, particularly of UVB radiation, are also well known and a medical concern.
Most of the devices designed for phototherapy, both in the UVA and UVB, are table top projectors for irradiating the face or feet, or booth or chamber types of devices (solaria). Various UV booth apparatuses are revealed in U.S. Pat. Nos. 4,095,113, 4,103,175, 4,100,415, 4,703,184, 4,177,384, 4,959,551, 4,469,951 and 4,309,616. All of these devices rely upon tubular fluorescent or tubular mercury bulbs as UV sources. The booths are generally composed of multiple banks of bulbs, and irradiate large areas, usually the whole body. Large unaffected portions of the body can be protected with draping or wrapping materials, but this is impractical for most clinical use. The large area (whole body or limb) radiation pattern of these devices is a result of the emission characteristics of the light sources. The diffuse, lambertian emission patterns from these elongated, cylindrical bulbs are difficult to aim or direct to specific areas. To achieve sufficient radiation levels to provide therapeutic affect, large numbers of bulbs are required to achieve treatment times within practical limits. It is common for a booth to have 24 to 48 bulbs to achieve these practical fluence levels.
Generally, the dose of UVB radiation administered in a booth is limited by erythemal (sunburning) action. The absolute amount of UVB that a given person can tolerate before burning varies by skin type and prior exposure. It also varies with the composition of the UVB, because shorter wavelengths have greater erythemal activity. Normally, before treatment is given, the minimum erythemal dose (MED) for each patient is determined by applying different radiation doses in small patches to healthy tissue. These patches indicate the amount of energy (usually expressed in mj/lcm2) that will result in sunburning the patient. It is typical for the patches to be viewed at 24 hours, and the patch that is slightly pink is considered the MED level. A single booth treatment starts at some percentage (often 70%) of this MED, and then may be increased in follow up sessions as tolerance builds up due to tanning. A typical cycle of treatments for therapeutic success in a booth is 15 to 30 treatments, usually administered in 2 to 3 treatments per week. The amount of radiation given in a given session is limited by the radiation exposure of the healthy tissue. Sunburning the entire body is not only painful, but also medically unwise.
A similar technique is used for UVA treatment, but the dose is called the MPD and the reading is generally 72 hours after exposure. In both cases, however, the MED or MPD is determined by radiation on healthy (non-lesional) tissue.
Much of the UVA therapy has been replaced by PUVA therapy, called photochemical therapy, where the photosensitizer psoralen or one of its derivatives is used with UVA radiation. PUVA treatment has proven to have long term oncological manifestations not seen with UVB treatment. However, when UVB treatment has not been successful, the alternative of PUVA does provide relief, albeit at a potential health risk.
It has been demonstrated that some lesional tissue (psoriatic plaque for example) can withstand much more UVB radiation than healthy tissue. This is largely due to the thickness of the plaque areas. However, the radiation delivered to the plaque in booth therapy is limited to the amount of radiation that the adjacent health tissue can withstand. There are three negative aspects of booth UVB treatment. First, the radiation is provided to both healthy and lesional tissue, thus increasing the total body UVB exposure. It has been demonstrated that this cumulative total body exposure has carcinogenic implications. Second, the low radiation threshold of healthy tissue limits the amount of radiation that may be delivered per session to the lesional areas. This sub-optimal dosage results in an increased number of treatments to achieve the cumulative lesional radiation required for therapeutic success. Third, the increased number of treatments that result from low plaque doses again increases the total body radiation received.
The article entitled xe2x80x9cAction Spectrum for Phototherapy of Psoriasisxe2x80x9d, by John A. Parrish, M.D. and Kurt F. Jaenicke, B.A., published in the Journal of Investigative Dermatology, Vol. 76, No. 5, p. 359-362 (1981) describes the psoriasis action spectrum from 253 nm to 313 nm. The results in this article indicate that radiation below 296 nm is highly erythemal but not therapeutic. The article also reports that the level of radiation to deliver 1 MED at 300 nm is about {fraction (1/10)}the radiation level required to achieve 1 MED at 313 nm. This confirms the higher erythemal activity of shorter wavelength UVB. Conventional UVB fluorescent sources provide UV radiation from 275-340 nm, a result of the fluorescent material bandwidth, and hence provide significant radiation of erythemal activity without therapeutic affect. Since a high proportion of this conventional flourescent radiation is non-therapeutic, but erythemally limiting, it necessitates a larger number of treatments.
The presence of the erythemally limiting but non-therapeutic radiation from conventional sources has led to the development of more effective UVB lamps for phototherapy. Sources of monochromatic radiation at 308 nm are available in the form of excimer lamps (U.S. Pat. No. 5,955,840). Also, tubular fluorescent lamps with nearly monochromatic output at 311 nm (U.S. Pat. No. 4,354,139) are available. Both these lamp sources suffer from the disadvantages of large area radiation, i.e. erythemal limits per treatment and healthy tissue radiation. However, many reports are available on the advantages of monochromatic UVB from these lamps. One advantage is the lack of non-therapeutic, erythemal radiation below 296 nm. This allows more of the delivered UVB radiation to be of therapeutic value before the MED is reached. Conventional UVB bulbs which operate in the broad range of 275-340 nm may provide undesirable radiation which promotes cellular proliferation.
As opposed to this large area radiation, targeted phototherapy is the application of radiation to specific areas, defined by the geometry or exit aperture of a delivery device. The radiation dose is generally, although not necessarily, constant through out the application to a lesion. The dose administered during an irradiation cycle is known, and the boundary of the irradiated area is known. It may be thought of as placing a penlight against the skin. The area is known to be the exit area of the penlight, and, in the case of targeted phototherapy, the dose may be controlled. Repeating this pattern of the penlight exit face over a lesion allows for complete coverage of the lesion.
Tubular fluorescent lamps in general cannot be effectively used for targeted radiation delivery. This is due to the difficulty in collecting the light from these elongated, diffuse sources, and focusing it onto the skin or into an optical guide. Targeted, or spot delivery of radiation in general requires that the light source be collimated or be of a small intense arc that allows efficient fiber optic coupling. Targeted UV phototherapy systems typically employ lasers and are very expensive.
Monochromatic radiation at 308 nm can be provided by xenon chloride excimer lasers, and such sources are capable of directed site delivery as a result of their coherent beams. The disadvantage of such sources is the high cost of equipment and associated maintenance. They nominally sell in the hundreds of thousands of dollars, and contain high-pressure toxic gases that must be regularly exchanged.
It is an object of the present invention to provide a new and improved targeted UV phototherapy apparatus and method.
According to one aspect of the present invention, an apparatus for directing targeted UV radiation to a predetermined area of a patient to be treated is provided, which comprises a UV radiation source for emitting UV radiation in a first wavelength, a phosphor element separate from the source for converting the UV radiation in the first wavelength to a different UV wavelength, a radiation directing assembly for directing radiation from the UV source to the separate phosphor element, and an exit aperture for directing radiation emitted from the phosphor element onto a predetermined target area of a patient.
Preferably, a handpiece is provided which has an internal chamber in which at least the phosphor element is mounted, and the exit aperture is provided at one end of the handpiece. In one embodiment of the invention, the UV radiation source is separate from the handpiece, and the radiation directing assembly comprises an optical guide connecting the UV source to an inlet end of the handpiece. In an alternative embodiment, the UV source is mounted in the handpiece itself, facing the phosphor element, and the radiation directing assembly comprises a reflector for directing radiation from the UV source onto the phosphor element.
In a preferred embodiment of the invention, the UV source comprises a source of UVC radiation, and the phosphor element is of a luminescent material for converting UVC radiation to UVB or UVA radiation. Different phosphor elements may be provided for UVB and UVA radiation, and selectively connected to the source depending on the type of UV radiation to be used for treatment. The UVC source may be a deuterium lamp, rare gas discharge lamp, mercury lamp, mercury short arc lamp, or high intensity discharge (HID) mercury halide lamp.
According to another aspect of the present invention, a method of treating lesional tissue is provided, which comprises the steps of:
directing radiation from a source of UV radiation onto a separate phosphor element;
converting the radiation received from the source into UV radiation of a predetermined different wavelength in the phosphor element; and
directing the converted radiation from the phosphor element onto a predetermined area of lesional tissue through an exit aperture of predetermined shape and dimensions.
In this invention, the phosphor is removed from inside of the lamp and placed near the area to be irradiated. This retains the high conversion efficiency and wavelength selection flexibility of phosphors, without the short lifetime problems of placing such phosphors in a mercury plasma environment. By moving the phosphor outside the lamp and placing it close to the area to be treated, targeted UV radiation is possible, and the lifetime of the phosphor is also significantly increased. This technique also enables the output efficiency of the phosphor to be improved by increasing the energy density of the exciting radiation. The term phosphor as used herein refers to an inorganic material capable of being excited by a source of radiation and emitting a second radiation of longer wavelength.
This invention is a considerable improvement over traditional whole body irradiation in phototherapy booths using fluorescent lamps. In a tubular fluorescent lamp, a phosphor material is coated on the inside of the tube and a baking process is used to drive out organic binders used to make the coating adhere to the tube. This can cause some oxidation of the phosphor, making it less efficient. The phosphor and lamp lifetime is also affected by the inherent design characteristics of fluorescent tubes. Output decay is caused by absorption of mercury by the phosphor, and considerably reduces phosphor lifetime. A typical useful lifetime for fluorescent lamps used in phototherapy booths is only 500 to 2000 hours, and 24 or more lamps are typically used in such booths. Thus, lamp replacement is a significant expense. Additionally, light collection and concentration from such lamps is very difficult, so an individual to be treated can be exposed for only a short time interval to avoid damage to healthy skin, or must be draped to cover healthy skin areas.
In contrast, the present invention provides targeted radiation directed only onto a lesional area of the skin, using only one UV lamp, and significantly increases the effective phosphor lifetime, as well as the output efficiency.